The fastest predator on Earth: star-nosed mole


Eimer’s organ: touch receptors - 120 milliseconds to identify and consume prey

The Big Picture: Perception to Behavior




  • Sensory processes begin with stimuli
    • stimuli are forms of energy


  • Receptors alert nervous systems
    • use action potentials
    • results in a ‘sensation’


  • After a stimulus is processed, a motor response may be generated

Sensory Pathways



  • Neurons =


  • Most organelles inside cell body
    • includes nucleus


  • Highly branched extensions, called dendrites, receive signals


  • Most neurons have a single axon to transmit signals
    • transmit pulses of electrical current
    • terminals connect cells

(1) Sensory Reception



  • Sensory pathway starts with perception of sensations


  • Sensory pathways have four basic functions:
    • reception, transduction, transmission, perception


  • (1) Sensory reception:
    • sensory cells are specialized neurons
    • inside or outside body
    • detection of a stimulus

(2) Sensory Transduction: Converting signals



  • Transduction:
    • strength of stimulus determine how much


  • Stimulus receptors change flow of ions across membranes
    • opens/closes ion channels
    • Ca2+, Na+, K+


  • Membrane potential: gradient that forces ions to passively move in one direction
    • can be processed by central nervous system

(3) Sensory Transmission: action potentials (nerve impulse)





  • Transmission:


  • Action potential:
    • caused by change in membrane potential


  • Receptor generates action potentials that travel to central nervous system
    • large stimulus = more action potentials

Action Potential further explained…

(4) Sensory Perception: Processing the stimulus




  • Perception:


  • How does the brain know the difference in stimuli?
    • action potentials are just electrical signals…


  • Action potentials reach brain via dedicated neural pathways
    • brain distinguishes stimuli on the path they arrive

If a tree falls in the woods……


Animal sensory receptors: Mechanoreceptors




  • Response to touch, stretch, motion and sound
    • Receptors sense physical deformation


  • Ion channels linked to structures that end outside cell
    • hair or cilia
    • bending/stretching structure generates response


  • Touch receptors often embedded in tissue

Diversity of mechanoreceptors on mouse face



Animal sensory receptors: Chemoreceptors



  • (1) Transmit information about solute concentration
    • detect change in blood solutes → stimulate thirst


  • (2) Respond to individual kinds of molecules
    • glucose, O2, CO2, amino acids


  • Stimulus molecule binds to a chemoreceptor


  • Chemoreceptor becomes more or less permeable to ions
    • silk worms detect pheromones from females several kilometers away

Taste and smell rely on chemoreceptors


Taste and smell rely on chemoreceptors


Animal sensory receptors: Electromagnetic




  • Receptors that detect light, electricity and magnetism


  • Animals create & detect electromagnetic energy to hunt


  • Used by animal kingdom to migrate
    • proteins can sense Earth’s magnetic fields
    • insects, birds & mammals

Animal sensory receptors: Electromagnetic




  • Receptors that detect light, energy and magnetism
    • may also create & detect electromagnetic energy



  • Used widely by animals to sense prey
    • 16% of fish species use electroreceptors to detect bioelectric fields from prey

Animal sensory receptors: Thermoreceptors



  • Receptors detect heat and cold


  • Hot pepper science has really helped!!!
    • Receptors that respond to capsaicin also respond to high temperatures
    • open a calcium channels
    • taste ’hot": activate same receptors as hot soup
    • opposite for ‘cold’ flavor


  • Mammals: thermoreceptors for specific temperatures
  • Venomous snakes: infrared receptors to detect ‘warm’ prey

Animal sensory receptors: Pain





  • Pain receptors (nocioreceptors) detect stimuli that reflect harmful conditions
    • damaged or inflammed tissues
    • gene mutations can cause C.I.P.


  • Respond to damaged/inflamed tissues
    • perceived as pain
    • trigger defenses (withdraw)